diff -r 889301acc299 -r 7d1ff2f621c7 src/cargopacket.cpp
--- a/src/cargopacket.cpp	Sun Feb 03 20:34:26 2008 +0000
+++ b/src/cargopacket.cpp	Mon Mar 10 15:26:39 2008 +0000
@@ -37,7 +37,7 @@
 	this->count = 0;
 }
 
-bool CargoPacket::SameSource(CargoPacket *cp)
+bool CargoPacket::SameSource(const CargoPacket *cp) const
 {
 	return this->source_xy == cp->source_xy && this->days_in_transit == cp->days_in_transit && this->paid_for == cp->paid_for;
 }